Emotions play an important role in the regulation and expression of parenting behavior in female primates. Increased arousal in response to infant stimuli can facilitate interactions with infants early in a female’s life and provide opportunities for learning and practicing parenting skills. Infant-related arousal can also facilitate the expression of parental responses to a female’s own offspring later in life. Negative emotions such as anxiety and fear can elicit protective parental behaviors. Maternal anxiety is elicited by momentary separation from the infant and concerns about infant safety. Free-ranging rhesus macaque (Macaca mulatta) females show higher cortisol responses to stress when they are lactating than when they are cycling. The lactation-associated increase in cortisol responsiveness to stress is greater for low-ranking than for high-ranking mothers, suggesting that lactation carries greater costs to low status females. Heightened reactivity to stress during lactation may interfere with the expression of parental behavior. In addition, it may impair immune function and increase vulnerability to infectious diseases. Consistent with this, the probability of mortality for free-ranging adult rhesus females peaks during the birth season, whereas adult males are most likely to die during the mating season.